It is known to assemble mechanical drives comprising a drive (or driven) shaft and rotatable parts or components which are subjected to repeated fluctuations in load. For example, inserter machines, such as the 8300 Inserter Series manufactured by the assignee of the present invention, include bursting and sheet feeding apparatus which continually operate in rapid stop and go, or deceleration and acceleration movement of the mechanical drives. A basic problem inherent with such operation is that over a period of operation the mechanical drive components wear and become loose on the shaft causing the components to slip and the operation to malfunction.
Various methods have been used to prevent the mechanical drive components, such as pulleys, sprockets or gears, from slipping on the drive shaft. One method that is well known is to secure the component to the drive shaft using a set screw passing through the component or through an extended portion of the hub of the component. The set screw is tightened against the drive shaft to lock the component in place. Variations of this method include the use of a “D” shaft whereby the screw is tightened against the flat portion of the shaft. Typically, the “D” hole of the component is sized and matched to the “D” shape of the shaft such that it just slips over the shaft. Although such methods are suitable for securing the components to the drive shaft, experience has shown that they do not prevent the assembled component from becoming loose on the shaft and moving from the prescribed lateral position. The continuous fluctuations in load, such as the stop and go movement caused by clutch and brake operation in a bursting apparatus, eventually causes the screw to loosen or the shaft to wear and eventually causes a failure in the apparatus. Another problem with tightening the set screw against the drive shaft is that the screw notches the drive shaft and the notches may restrict further adjustments to the location of the component on the drive shaft.
A more reliable method of securing a drive component to the drive shaft is positioning the component, such as a pulley, laterally on the drive shaft during assembly, drilling a tapered hole through the pulley and its hub and the drive shaft, and banging a tapered pin into the hole so that the component becomes integral with the drive shaft. This provides an assembly capable of handling repeated fluctuations in load. One disadvantage with this method is that it is not suitable for use with nonmetal components on machines having torque loads such as inserters. Another disadvantage of this method is that although it is more reliable for preventing a loosing of the component on the drive shaft, it is not suitable for after assembly adjustment or replacement of the component. Because the hole is drilled through the component and shaft at the same time during assembly, it is difficult to replace a worn component without replacing the shaft. Furthermore, this method does not leave room for error because once the hole is drilled into the drive shaft mistakes in the lateral positioning of a component on the shaft cannot easily be corrected. Any position adjustments may require replacement of the drive shaft. Another problem in this area is that commercially manufactured drive components typically are manufactured with a round hole. When the component is to be used on a “D” shaft, a special part must be ordered or a hub with a “D” hole must be inserted into a bored out hole in the component. Generally, the hubs which are suitable for use with metal components are not suitable for use with softer material such as urethane.
One attempt to overcome the above-noted problems of mounting a mechanical drive component to a shaft can be found in commonly assigned U.S. Pat. No. 5,052,842 to Karel J. Janatka. Even though the invention of this patent was an improvement over the existing art at the time of the invention, it still suffers from some notable drawbacks when applied to modern high-speed inserter systems. For instance, this invention disclosed a two part clamping member consisting of a clamp collar and a separate hub member wherein the hub member receives into the clamp collar around a shaft extending therethrough. However, with this arrangement, it has been found that it is not adequate for high performance motion control demanded by modem high-speed inserter systems, such as the Pitney Bowes APS inserter system. This is because in such high speed inserter systems, typical accelerations and decelerations at the paper path routinely exceed 8 G-forces. And typical duty cycles for a complete start and stop motion profile are typically 5 cycles/second, and some may even be higher, such as, backstop motors that execute at 10 cycles/second. To accomplish these aggressive motions, mechanisms must be designed to minimize inertia and servo motors have to be selected that have coupling ratios that are calculated to minimize motor heating. It is noted that motor heating is usually the limiting factor for accomplishing continuous duty high-performance incremental motion profiles.
Thus, in such high-speed inserter systems that require aggressive incremental motion control, it is desirable to tightly couple driven mechanism loads to their respective driven shaft. However, traditional clamping methods, such as the clamping collar disclosed in U.S. Pat. No. 5,052,842, are not adequate for such high performance motion control since the clamp collar introduces significant inertia, thus increasing peak and RMS torque required of the motors driving the shafts. This ultimately increases motor heating and decreases the life expectancy of the motors. Further, the two part clamp assembly of this invention still requires the use of a D-shaped shaft.
It is also noted that in addition to what is described above, other methods of mounting drive components to hubs are known but require special assembling or tooling.